The invention relates to a bulk silo with an outlet chamber, from whose upper area a generally open ventilation line extends which is provided with a valve part of protection against flooding.
Usually, the ventilation line of silo emptying chambers extends essentially exclusively vertically upward, so that any penetrating bulk material can fall back down and out without clogging the ventilation line (e.g. DE - OS No. 26 19 933). For reasons of stability, such vertical ventilation lines can generally be placed only on the outer wall of the silo, so that they are only suitable for ventilating an outlet chamber located centrally on the silo bottom if a lateral auxiliary chamber is provided between this central chamber and the ventilation line located on the silo wall (e.g. DE - PS No. 26 57 597). The expense for this auxiliary chamber can be avoided if the ventilation line is not positioned so that it rises exclusively vertcially, but rather in some other way, especially falling to an outlet path for the material provided below the silo bottom (e.g. DE - AS No. 28 49 014), which, however, necessitates a valving part in the ventilation line to prevent it from being flooded and to prevent the associated danger of clogging. In the initially cited instance this part is mechanically controlled and only closed if the possibility of flooding the ventilation line is created by closing or occluding the silo outlet, However, the valving parts and the devices for their active control are expensive.
The present invention has the task of creating an inexpensive, operationally safe and easy-to-service device for the protection of a ventilation line which does not rise exclusively vertically.
The present invention solves this task by constructing the closing part as a float valve whose float cage is provided with an aeration device in the area under the float.
Float valves are known in the fluid transfer art, even in the form preferred by the invention, in which the float valve opening is located above the float forming the valve body. It is also known that bulk material can be put in a fluid-like state by means of aeration and that therefore some elements known in the area of fluid transfer can be applied to bulk material fluidized in transfer. However, the use of a float valve for solving the basic problem of the invention was not obvious. The analogy between the transfer of fluids and the transfer of fluidized bulk materials always breaks down when the fluidized state of the bulk material is not assured under all operating conditions and when the smooth operation of the part in question is endangered by the appearance of unfluidized bulk material. When a float valve is used in the outlet chamber of a bulk silo, the appearance of insufficiently fluidized material must be reckoned with for two reasons. Firstly, it is known that a complete fluidization of the material contained in the outlet chamber of a silo can be depended upon only in the ideal situation, namely, in the stationary flow state of easily fluidizable materials, while in the starting state. When the removal of material from the silo is cut off, there is a danger that the air entering at the bottom of the outlet chamber into the material will blow free passageways, so-called rat or blow holes, in the material through which it escapes without fluidizing the material located at the sides of the passageways. There is always the possibility, even in an advanced aeration state, that the totally fluidized mass of material contains agglomerates of unfluidized material. If such unfluidized material passes in the direction of the float cage, it can settle there, block the movement of the float and thus disrupt an orderly operation. Secondly, it must be reckoned with that the fluidized material passing into the float valve will settle there, solidify due to the escape of air contained in it and finally harden, until a smooth operation of the valve becomes questionable.
These dangers avoided by the invention by providing the float cage with an aeration device in the area under the float. This device is not intended to assure that the material reaching this point is sufficiently aerated, because this material had already been fluidized previously in the outlet chamber or can also, if it is a matter of a piece of non-fluidized material, no longer be fluidized in the vehemence of its movement during the brief time of its entry into the float cage by means of the aeration devices provided there. Rather, the invention has recognized that the possibility can simply not be excluded that non-fluidized material will be in the vicinity of the float valve; however, this can be accepted, because the aeration devices assure that this material is subsequently removed, so that no permanent disturbance of the valve will occur.
If there is a sudden rise of the material in the outlet chamber, actuating the float valve, this rise comes primarily from below. It would therefore be obvious to utilize the impulse coming from below, just as in fluid float valves, along with the hydrostatic upward impulse for the closing operation of the float valve. However, the invention disregards this in an advantageous embodiment and makes the float cage closed on its underside in order to achieve the advantage that the particulate material can flow into the float cage only from the side, which reduces the probability that not enough flowable material passes into it.
In the embodiment of the float cage with a closed underside the aeration device is preferably constructed as a porous area provided at the top of the closed undersurface through which porous area compressed air is constantly forced and which is free at the sides for the run-off of the fluidized material on it.
The aeration device of the invention is preferably constantly loaded with compressed air, even if no acute danger of flooding is present. The increased air requirement necessiated by this negligibly small in comparison with that of the other aeration devices of a conventional silo.